1. Field of the Invention
This invention relates to a supporting device for mounting a protective cover to shield a cutting blade of a cutting machine, more particularly to a supporting device which is easily operated to be tightened firmly to a position of use or a retreat position.
2. Description of the Related Art
In a conventional table cutting machine, such as a circular saw machine, a supporting device is disposed adjacent to a circular saw blade for mounting a protective cover to shield the circular saw blade. The supporting device is detachably disposed on a worktable so as not to obstruct specific working operation, such as cutting a slot in a workpiece.
Referring to FIG. 1, a conventional supporting device 10 includes a fixed mount unit 11, a tightening mount unit 12 movably disposed on the fixed mount unit 11, and a control unit 13 disposed between the fixed and tightening mount units 11,12. The fixed mount unit 11 has a fixed mount 111 secured on a tabletop (not shown) of a cutting machine. The fixed mount 111 has a sliding slot 112 in a side thereof for fitting of a tightening mount unit 12. The tightening mount unit 12 has a tightening plate 121 which is fitted to the sliding slot 112, a cam follower piece 122 which is embedded into the tightening plate 121, and a limiting pin 123 which extends outwardly of the tightening plate 121. The control unit 13 has a tightening bolt 131, a cam piece 132 which meshes with the cam follower piece 122, a handgrip 133 which extends radially from the cam piece 132, and a limiting protrusion 134 which is disposed on the cam piece 132 to abut against the limiting pin 123. A clearance is present between the tightening plate 121 and a side of the fixed mount 111 for accommodating a lower portion of a supporting frame 1. An upper portion of the supporting frame 1 is adapted to hold a protective cover (not shown). When the user operates the handgrip 133 to rotate the cam piece 132, the cam follower piece 122 is pressed toward the fixed mount 111 so as to tighten the supporting frame 1 for positioning the protective cover on the cutting machine. However, the cam piece 132 may be rotated to cause movement of the cam follower piece 122 away from the tightening plate 121 when the machine is vibrated during the cutting operation, thereby resulting in undesired detachment of the supporting frame 1 from the tightening mount unit 12.
Referring to FIG. 2, another supporting device 20 includes a mounting unit 21, a supporting frame unit 22 and a control unit 23. The mounting unit 21 has a fixed mount 211 and a tightening plate 212. The supporting frame unit 22 has a supporting frame 221 which is disposed between the fixed mount 211 and the tightening plate 212, and which has an arcuate slot 2211. The control unit 23 has a tightening bolt 231 which extends through the arcuate slot 2211 and into the fixed mount 211, two washers 232 which are sleeved on the tightening bolt 231, a guide pin 233 which is disposed on the tightening bolt 231, and a cam actuator 234 which is sleeved on the tightening bolt 231 at one end thereof, and which has a handgrip at the other end. The cam actuator 234 has a spirally extending groove 2341 which surrounds the tightening bolt 231 for guiding movement of the guide pin 233. Thus, when the user rotates the cam actuator 234, the cam actuator 234 can press the tightening plate 212 via the washers 232 towards the fixed mount 211 so as to tighten the supporting frame 221. However, undesired loosening of the supporting frame 221 may occur after a long-term use.